Keep Calm and Carry On was a propaganda poster produced by the British government in 1939 during the beginning of the Second World War, intended to raise the morale of the British public in the event of invasion. Seeing only limited distribution, it was little known. The poster was rediscovered in 2000 and has been re-issued by a number of private sector companies, and used as the decorative theme for a range of other products. There are only two known surviving examples of the poster outside government archives. The designer of the original poster is not known.

The poster has appeared on the walls of places as diverse as the prime minister's strategy unit at 10 Downing Street, the Lord Chamberlain's office at Buckingham Palace, and the United States embassy in Belgium. The Manleys sold some 41,000 facsimile posters between 2001 and 2009.

The poster and its parodies have appeared in almost every channel open to graphic design and graphical parody, ranging from the political messages to cute slogans. Many versions of it reference other aspects of popular culture, from the wedding of Prince William and Catherine Middleton to the Mario videogames, with altered text, colours and iconography.